1. Field of the Invention
The invention pertains to a forward bearing arrangement for the tilting cab of a truck, with at least two brackets fastened to the vehicle frame, on which the cab is supported at the front by way of elastic bearings mounted on bearing axles which are aligned with each other, which bearings are mounted in bearing shells fastened to the floor of the cab.
2. Description of the Related Art
Bearing arrangements for tilting cabs of trucks are already known (e.g., DE 195 37 722 A1, EP 0 635 419 B1). A bearing arrangement of this type is based on the following problems: To achieve a sufficiently comfortable ride, the cab bearings must allow the longest possible distances, but these are predetermined by the design and by the material of the elastic bearings. Relatively soft elastic bearings, which allow relatively large spring excursion, however, turn out to be disadvantageous when the cab is tilted.
In the bearings of the tilting cab of a truck, various loads, i.e., functionally superimposed loads, are always to be expected at the forward bearing points. While the vehicle is being driven, torsional loads of approximately xc2x110xc2x0 occur, upon which radial and axial loads are superimposed. When necessary, however, the cab must also be tilted at the same bearing points, in which case a torsional load of approximately 70xc2x0 must be handled. In addition, there are also cardanic loads.
Pure plain bearings have not proven to be sufficiently long-lived at this installation point, because the continually alternating loads in a relatively small area of the bearing (point load), which area is always the same, leads to premature wear, even when the bearings are designed to be greased. In addition, plain bearings are difficult and expensive to produce because of the very close manufacturing tolerances, and they do not have any damping properties at all. Because plain bearings have no elasticity, furthermore, high edge pressures also occur under cardanic load.
It is therefore the object of the invention to design a forward bearing arrangement for a tilting cab in such a way that the elastic bearings provide a comfortable spring suspension of the cab but at the same time allow the cab to be tilted easily.
To achieve this object, in accordance with the invention the bearing includes a rubber bearing with a plain bearing coaxial to it. It is advantageous here that the customers"" requirements for comfort during operation of the vehicle, for a long service life (vehicle life), and simultaneously for favorable torsional properties when the cab is tilted are all accommodated when the forward bearing arrangement consists of this combination of a rubber bearing and a plain bearing.
It is also advantageous that the functions of this type of bearing are separated between driving and tilting, which gives the bearing superior properties in each category. In terms of vehicle operation, the use of a rubber bearing satisfies to the highest degree the customers"" requirements for freedom from maintenance, long service life, economy, and a comfortable ride, whereas, when the cab is tilted, the plain bearing is able to handle by itself the rotational movements of approximately 70xc2x0 and must therefore do no more than withstand the required number of load cycles of 1,500 tilts.
In accordance with another essential feature of the invention, it is provided that the rubber bearing is mounted on the bearing axle and the plain bearing is mounted between the rubber bearing and the bearing shell radially on the outside. Because the two different functions are separated, both the rubber bearing and the plain bearing can be designed at low cost to meet the minimum appropriate requirements.
In accordance with another essential feature, an arresting device is provided to prevent the plain bearing from rotating. By means of an arresting device of this type, it is therefore possible to xe2x80x9cdeactivatexe2x80x9d the plain bearing, as it were, while the vehicle is being driven.
It is also provided that the arresting device is under pretension and allows the plain bearing to rotate once a certain predetermined force is exceeded. As an arresting device, the plain bearing has at least one recess in the outside circumference, in which a spring-loaded element engages. It is advantageous for this element to be ball.
An arresting device of this type with spring-loaded elements on the outside circumference of the outer part of the rubber bearing which latch in a positive, form-locking manner has the effect of deactivating the plain bearing, which is on the outside. While the truck is being driven, the spring-loaded elements arrest rotation of the plain bearing relative to the rubber bearing and thus transmit all of the torsional movements introduced up to a certain defined torsion angle to the rubber bearing in a positive, form-locking manner. The main loads during driving, namely, the torsional loads of approximately xc2x110xc2x0, upon which radial and axial loads are superimposed, as well as the allowable manufacturing tolerances are absorbed by the maintenance-free rubber bearing.
The larger torsion angles associated with the tilting of the cab lead to the unlatching of the elastic elements from their recesses and thus to the activation of the plain bearing. From this moment, the rubber bearing is free of torsional load, and the spring-loaded elements now slide over the circumference of the outer bearing part. The following torsional movement is then handled exclusively by a maintenance-free plain bearing, with a contact layer consisting of, for example, a PTFE component (without lubrication). Thus the plain bearing is under load only when the cab is tilted and not while the truck is being driven, which means that service life problems in this area can be excluded.
According to another embodiment, it is provided that each ball is located together with a compression spring in a bore in a screwed-in part.
According to an advantageous embodiment, it is provided that the rubber bearing consists of an inner bush and an outer bush with a rubber element between them. Readily available, standard rubber bearings of this type can be used; the only point requiring attention is the coordination of the diameters of the two bearings to each other, which should present no difficulty.
In accordance with another design, it is provided that the rubber bearing and the plain bearing are held in place in a bore in the bearing shell by at least one lock washer.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.